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375 results for “X* chromosome”
Data from: A rare exception to Haldane’s rule: Are X chromosomes key to hybrid incompatibilities?
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Data from: The large-X effect in plants: increased species divergence and reduced gene flow on the Silene X-chromosome
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Data from: Introgression across hybrid zones is not mediated by Large X-effects in green toads with undifferentiated sex chromosomes
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Genetic architecture of individual variation in recombination rate on the X-chromosome in cattle
<p class="Standard"><span>Meiotic recombination is an essential biological process that ensures proper chromosome segregation and creates genetic diversity. Individual variation in global recombination rates has been shown to be heritable in several species and variants significantly associated with this trait have been identified. Recombination on the sex chromosome has often been ignored in these studies although this trait may be particularly interesting as it may correspond to a biological process distinct from that on autosomes. For instance, recombination in males is restricted to the pseudo-autosomal region (PAR). We herein used a large cattle pedigree with more than 100,000 genotyped animals to improve the genetic map of the X-chromosome and to study the genetic architecture of individual variation in recombination rate on the sex-chromosome (XRR). The length of the genetic map was 46.4 and 121.2 cM in males and females, respectively, but the recombination rate in the PAR was 6 times higher in males. The heritability of CO counts on the X-chromosome was comparable to that of autosomes in males (0.011) but larger than that of autosomes in females (0.024). XRR was highly correlated (0.76) with global recombination rate (GRR) in females, suggesting that both traits might be governed by shared variants. In agreement, a set of eleven previously identified variants associated with GRR had correlated effects on female XRR (0.86). In males, XRR and GRR appeared to be distinct traits, although more accurate CO counts on the PAR would be valuable to confirm these results. </span></p>
Data from: On the Coyne and Orr-igin of species: effects of intrinsic postzygotic isolation, ecological differentiation, X-chromosome size, and sympatry on Drosophila speciation
Coyne and Orr found that mating discrimination (premating isolation) evolves much faster between sympatric than allopatric Drosophila species pairs. Their meta-analyses established that this pattern, expected under reinforcement, is common and that Haldane's rule is ubiquitous in Drosophila species divergence. We examine three possible contributors to the reinforcement pattern: intrinsic postzygotic isolation, dichotomized as to whether hybrid males show complete inviability/sterility; host-plant divergence, as a surrogate for extrinsic postzygotic isolation; and X chromosome size, whether roughly 20% or 40% of the genome is X-linked. We focus on "young" species pairs with overlapping ranges, contrasted with allopatric pairs. Using alternative criteria for "sympatry" and tests that compare either level of prezygotic isolation in sympatry or frequency of sympatry, we find no statistically significant effects associated with X chromosome size or our coarse quantifications of intrinsic postzygotic isolation or ecological differentiation. Although sympatric speciation seems very rare in animals, the pervasiveness of the reinforcement pattern and the commonness of range overlap for close relatives indicate that speciation in Drosophila is often not purely allopatric. It remains to determine whether increased premating isolation with sympatry results from secondary contact versus parapatric speciation and what drives this pattern.
Data from: Experimental swap of Anopheles gambiae's assortative mating preferences demonstrates key role of X-chromosome divergence island in incipient sympatric speciation.
Although many theoretical models of sympatric speciation propose that genes responsible for assortative mating amongst incipient species should be associated with genomic regions protected from recombination, there are few data to support this theory. The malaria mosquito, Anopheles gambiae, is known for its sympatric cryptic species maintained by pre-mating reproductive isolation and its putative genomic islands of speciation, and is therefore an ideal model system for studying the genomic signature associated with incipient sympatric speciation. Here we selectively introgressed the island of divergence located in the pericentric region of the X chromosome of An. gambiae s.s. into its sister taxon An. coluzzii through 5 generations of backcrossing followed by two generations of crosses within the introgressed strains that resulted in An. coluzzii-like recombinant strains fixed for the M and S marker in the X chromosome island. The mating preference of recombinant strains was then tested by giving virgin recombinant individuals a choice of mates with X-islands matching and non-matching their own island type. We show through genetic analyses of transferred sperm that recombinant females consistently mated with matching island-type males thereby associating assortative mating genes with the X-island of divergence. Furthermore, full-genome sequencing confirmed that protein-coding differences between recombinant strains were limited to the experimentally swapped pericentromeric region. Finally, targeted-genome comparisons showed that a number of these unique differences were conserved in sympatric field populations, thereby revealing candidate speciation genes. The functional demonstration of a close association between speciation genes and the X-island of differentiation lends unprecedented support to island-of-speciation models of sympatric speciation facilitated by pericentric recombination suppression.
Data from: 'Escaping' the X chromosome leads to increased gene expression in the male germline of Drosophila melanogaster
Genomic analyses of Drosophila species suggest that the X chromosome presents an unfavourable environment for the expression of genes in the male germline. A previous study in D. melanogaster used a reporter gene driven by a testis-specific promoter to show that expression was greatly reduced when the gene was inserted onto the X chromosome as compared with the autosomes. However, a limitation of this study was that only the expression regulated by a single, autosomal-derived promoter was investigated. To test for an increase in expression associated with 'escaping' the X chromosome, we analysed reporter gene expression driven by the promoters of three X-linked, testis-expressed genes (CG10920, CG12681 and CG1314) that were inserted randomly throughout the D. melanogaster genome. In all cases, insertions on the autosomes showed significantly higher expression than those on the X chromosome. Thus, even genes whose regulation has adapted to the X-chromosomal environment show increased male germline expression when relocated to an autosome. Our results provide direct experimental evidence for the suppression of X-linked gene expression in the Drosophila male germline that is independent of gene dose.
Data from: Quantifying the relative contributions of the X chromosome, autosomes, and mitochondrial genome to local adaptation
During local adaptation with gene flow, some regions of the genome are inherently more responsive to selection than others. Recent theory predicts that X-linked genes should disproportionately contribute to local adaptation relative to other genomic regions, yet this prediction remains to be tested. We carried out a multi-generation crossing scheme, using two cline-end populations of Drosophila melanogaster, to estimate the relative contributions of the X chromosome, autosomes and mitochondrial genome to adaptive divergence in four traits involved in local adaptation (wing size, and resistance to heat, desiccation, and starvation stresses). We found that the mitochondrial genome and autosomes contributed significantly to clinal divergence in three of the four traits. In contrast, the X made no significant contribution to divergence in these traits. Given the small size of the mitochondrial genome, our results indicate that it plays a surprisingly large role in clinal adaptation. In contrast, the X, which represents roughly 20% of the Drosophila genome, contributes negligibly – a pattern that conflicts with theoretical predictions. These patterns reinforce recent work implying a central role of mitochondria in climatic adaptation, and suggest that different genomic regions may play fundamentally different roles in processes of divergence with gene flow.
Data from: Bounds to parapatric speciation: A dobzhansky-muller incompatibility model involving autosomes, X chromosomes and mitochondria
We investigate the conditions for the origin and maintenance of postzygotic isolation barriers, so called (Bateson-)Dobzhansky-Muller incompatibilities or DMIs, among populations that are connected by gene flow. Specifically, we compare the relative stability of pairwise DMIs among autosomes, X chromosomes, and mitochondrial genes. In an analytical approach based on a continent-island framework, we determine how the maximum permissible migration rates depend on the genomic architecture of the DMI, on sex bias in migration rates, and on sex-dependence of allelic and epistatic effects, such as dosage compensation. Our results show that X-linkage of DMIs can enlarge the migration bounds relative to autosomal DMIs or autosome-mitochondrial DMIs, in particular in the presence of dosage compensation. The effect is further strengthened with male-biased migration. This mechanism might contribute to a higher density of DMIs on the X chromosome (large X-effect) that has been observed in several species clades. Furthermore, our results agree with empirical findings of higher introgression rates of autosomal compared to X-linked loci.
FIGURES 1–2. Endecous ubajarensis n in A new species of Endecous Saussure, 1878 (Orthoptera, Gryllidae) from northeast Brazil with the first X X 0 chromosomal sex system in Gryllidae
FIGURES 1–2. Endecous ubajarensis n. sp. habitus. 1—holotype male; 2—paratype female UBA02.
Restricted X chromosome introgression and support for Haldane's rule in hybridizing damselflies
<p>Contemporary hybrid zones act as natural laboratories for the investigation of species boundaries and allow to shed light on the little understood roles of sex chromosomes in species divergence. Sex chromosomes are considered to function as a hotspot of genetic divergence between species; indicated by less genomic introgression compared to autosomes during hybridisation. Moreover, they are thought to contribute to Haldane's rule which states that hybrids of the heterogametic sex are more likely to be inviable or sterile. To test these hypotheses, we used contemporary hybrid zones of <i>Ischnura elegans</i>, a damselfly species that has been expanding its range into the northern and western regions of Spain, leading to chronic hybridization with its sister species <i>Ischnura graellsii</i>. We analysed genome-wide SNPs in the Spanish <i>I. elegans</i> and <i>I. graellsii</i> hybrid zone and found (i) that the X chromosome shows less genomic introgression compared to autosomes and (ii) that males are underrepresented among admixed individuals as predicted by Haldane's rule. This is the first study in Odonata that suggests a role of the X chromosome in reproductive isolation. Moreover, our data adds to the few studies on species with X0 sex determination system and contradicts the hypothesis that the absence of a Y chromosome causes exceptions to Haldane's rule.</p>
Supplementary material 1 from: Lin C-X, Xu G-L, Jin Z-F, Liao W-B, Xu K-W (2022) Molecular, chromosomal, and morphological evidence reveals a new allotetraploid fern species of Asplenium (Aspleniaceae) from southern Jiangxi, China. PhytoKeys 199: 113-127. https://doi.org/10.3897/phytokeys.199.81292
Table S1
Inferring clonal somatic mutations directed by X chromosome inactivation status in single cells
<p>This repository contains large files for the reproduction of results described in the manuscript <strong>Inferring clonal somatic mutations directed by X chromosome inactivation status in single cells</strong>.</p>
Data from: X-chromosome meiotic drive in Drosophila simulans: a QTL approach reveals the complex polygenic determinism of Paris drive suppression
Meiotic drivers are selfish genetic elements that promote their own transmission into the gametes, which results in intragenomic conflicts. In the Paris sex-ratio system of Drosophila simulans, drivers located on the X chromosome prevent the segregation of the heterochromatic Y chromosome during meiosis II, and hence the production of Y-bearing sperm. The resulting sex-ratio bias strongly impacts population dynamics and evolution. Natural selection, which tends to restore an equal sex ratio, favors the emergence of resistant Y chromosomes and autosomal suppressors. This is the case in the Paris sex-ratio system where the drivers became cryptic in most of the natural populations of D. simulans. Here, we used a Quantitative Trait Locus (QTL) mapping approach based on the analysis of 152 highly recombinant inbred lines (RILs) to investigate the genetic determinism of autosomal suppression. The RILs were derived from an advanced intercross between two parental lines, one showing complete autosomal suppression while the other one was sensitive to drive. The confrontation of RIL autosomes with a reference XSR chromosome allowed us to identify two QTLs on chromosome 2 and three on chromosome 3, with strong epistatic interactions. Our findings highlight the multiplicity of actors involved in this intragenomic battle over the sex ratio.
Fig. 5 in Karyotype description and evidence of multiple sex chromosome system X X X X /X X Y in Potamotrygon aff. motoro and P. falkneri (Chondrichthyes: Potamotrygonidae) in the upper Paraná River basin, Brazil
Fig. 5. Karyotypes of female (a) and male (b) of Potamotrygon falkneri sample from Ilha Solteira, highlighting the sex chromosomes after conventional and the chromosomes marked by NOR. Scale bar = 10 m.
Fig. 6 in Karyotype description and evidence of multiple sex chromosome system X X X X /X X Y in Potamotrygon aff. motoro and P. falkneri (Chondrichthyes: Potamotrygonidae) in the upper Paraná River basin, Brazil
Fig. 6. Somatic metaphases of Potamotrygon aff. motoro, the population of Porto Rico (a), population of Ilha Solteira (b), identification of constitutive heterochromatin. Metaphases of Potamotrygon falkneri sample from Porto Rico (c) and Ilha Solteira (d), analysis of constitutive heterochromatin after C-banding technique.
Grasshopper genome reveals long-term conservation of the X chromosome and temporal variation in X chromosome evolution
<p>We present the first chromosome-level genome assembly of the grasshopper, <em>Locusta migratoria</em>, one of the largest insect genomes. We use coverage differences between females (XX) and males (X0) to identify the X chromosome gene content, and find that the X chromosome shows both complete dosage compensation in somatic tissues and an underrepresentation of testes-expressed genes. Remarkably, X-linked gene content from <em>L. migratoria </em>is highly conserved across four insect orders, namely Orthoptera, Hemiptera, Coleoptera and Diptera, and the 800 Mb grasshopper X chromosome is homologous to the fly ancestral X chromosome despite 400 million years of divergence, suggesting either repeated origin of sex chromosomes with highly similar gene content, or long-term conservation of the X chromosome. We use this broad conservation of the X chromosome to test for temporal dynamics to Fast-X evolution, and find evidence of a recent burst evolution for new X-linked genes in contrast to slow evolution of X-conserved genes. Additionally, our results reveal the X chromosome represents a hotspot for adaptive protein evolution related migration and the locust swarming phenotype. Overall, our results reveal a remarkable case of conservation and adaptation on the X chromosome.</p>
X chromosome in aged hematopoietic stem cells (HSC)
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Data from: Experimental swap of Anopheles gambiae's assortative mating preferences demonstrates key role of X-chromosome divergence island in incipient sympatric speciation.
Open the record for dataset details and reuse information.
Data from: X-chromosome meiotic drive in Drosophila simulans: a QTL approach reveals the complex polygenic determinism of Paris drive suppression
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Allen Brain Atlas
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International Brain Laboratory public data
The International Brain Laboratory public data releases expose standardized mouse decision-making experiments, including Neuropixels recordings, widefield calcium imaging, behavior, and session metadata accessed through the ONE API.
OpenNeuro
OpenNeuro is a free, open platform for sharing neuroimaging datasets, with public search, dataset pages, and download paths for web, S3, DataLad, and the OpenNeuro CLI.